This invention relates to apparatus for handling plastic film articles, and is more particularly directed to apparatus known as a vacuum wicketter, which picks up film articles such as plastic bags on a manufacturing line, and rotates to carry the same to a station where the plastic bags are placed on a wicket. Vacuum is applied to arms of the rotating wicketter at least from the pickup work station to the wicketting work station.
A conventional vacuum wicketter is of aluminum construction, having a two-part hub assembly and a plurality of vacuum arms. The hub assembly has a lower stationary part and an upper rotating part. Both of these are typically of cast aluminum. A bearing mounted on the lower stationary part permits rotation of the superposed upper rotating part. One or more vacuum lines are connected to the stationary hub part, and these connect to a semi-circular channel that is open on the upper surface of the stationary part.
The rotating hub part carries the vacuum arms which radiate from its circumference at an even spacing. Typically, there are eight arms spaced at 45 degrees. L-shaped passages in the rotating hub part have one end open to the circumference, which serves as a socket for the male end of the arm, and the other end open to the lower surface to communicate with the vacuum channel in the stationary part. This ensures that vacuum is applied while the respective arms rotate over an angular sector corresponding to the travel between the pickup station and the wicketting work station.
The arms are typically of aluminum and generally with a square or rectangular cross section. On each arm, the surface that faces in the direction of rotation has an elongated vacuum channel and a number of apertures or perforations to permit the arm to pick up and carry the plastic bag or other film articles. There is also typically a ceramic coating on this surface to withstand wear from friction of the plastic film against the arm.
However, with this construction there are a number of ensuing problems which can lead to break-downs or to long outages for maintenance. These problems arise largely because of plastic debris and dust which is sucked by the vacuum into the tubular arm, and which can accumulate and clog the apparatus.
The male portions of the wicketter arms have a circular cross section to fit into the sockets which are machined or drilled into the rotating hub portion. However, the remainder of the arm is of square or rectangular cross section. There are blind pockets where the circular and square cross-sectional portions meet, and these provide sites for collecting the plastic dust and debris. This matter quickly builds up and eventually will clog the arm, so that it will not operate as intended.
These tubular aluminum arms invariably have a plate that is either welded on or formed unitarily at the outer end of the arm, and which closes it off. Therefore, in order to clean dust and debris from the arm, it is necessary to remove the entire arm from the rotor hub. This takes considerable time and skill.
Furthermore, the ceramic surface on the aluminum arms eventually will wear off. At that point, the entire arm has to be removed and replaced, with the original arm being sent out for resurfacing. This is a rather expensive process, and there is significant down time for the arms to be removed and replaced.
Still another drawback with the conventional wicketter is that the two-part hub requires an additional bearing member between the stationary and rotating hub portions. This bearing can wear out, and it is difficult and time consuming job to replace it.